Orbital welding involves the use of a weld head that retains an electrode that revolves (orbits) around a workpiece as it welds the workpiece. The workpiece may be, for example, two cylindrical tubes having abutting end portions to be welded together end to end.
A known orbital welder includes a weld head that has two jaws defining an opening between the jaws. The weld head is placed in a welding position relative to the workpiece by moving the workpiece through the opening between the jaws. The workpiece is then in a circular work space inside a rotor. The rotor carries an electrode. When the weld head is actuated, the rotor rotates about the workpiece, and the electrode orbits about the workpiece. An electric arc is produced between the electrode and the workpiece. The heat of the arc welds the joint on the workpiece. Representative patents showing this general type of welder are U.S. Pat. Nos. 4,379,215 and 5,844,190, the entire disclosures of which are incorporated herein by reference.
The arc welding process produces a substantial amount of heat. Many known orbital welders have no internal cooling system and utilize plastic components that do not dissipate the heat well. This can degrade any plastic components of the weld head and thereby limit the number of workpieces the known weld head can weld before the weld head must be allowed to cool. Other known orbital welders have a water cooling system or other forced cooling system.
Heat generated during the welding process can also cause expansion of parts of the known weld head. For example, one portion of the known weld head includes a circular groove with a rectangular cross-sectional configuration. The rotor has a circular boss with a complementary rectangular cross-sectional configuration. The boss on the rotor is received in the groove. The slip fit engagement of the boss in the groove controls and guides movement of the rotor. As the parts of the known weld head heat up and expand, the rotor boss can bind on the portion of the known weld head that includes the groove.
One way to avoid binding is to add more clearance between the rotor and the insert; this produces, however, an electrode that does not orbit with a consistent arc gap.